For prison break escape: You are automatically given the rewards for the green boxes once the match ends. Usually they give you timed grenades, armor, or euros, with higher chances for better rewards the more you get them.
1-3 gives euros, but 3 gives the most at 500
4-6 gives 1, 3, and 7 day STG respectively
7-9 does the same for PPSh
10-12 gives Walther I think
13-15 gives L2A3
Or did I switch walther and L2A3? It usually doesn't matter though, most people just get 3 boxes and suicide.
DV extreme: 4 boxes will give you a chance to gain permanent Anaconda as well as various rewards up to 1000 euros.